As the number and complexity of wireless applications grow, there are increasing needs for circuits designed to operate at high frequencies, i.e., in the 1-25 GHz range for audio, visual, and data transmissions. Circuit materials are needed which combine low dielectric and conductor losses in this frequency range. Low temperature cofired ceramic tape (LTCC) is a well known technology for combining high conducting, low loss metallization (silver and gold) with reliable ceramic dielectric layers for dense packaging of IC circuits. The majority of present LTCC systems are composed of a borosilicate glass with a ceramic filler and an alumina filler which imparts high strength. The borosilicate glasses usually contain lead and alumina which contribute to unacceptable loss in db/in. when operated in a GHz range. Consequently ceramic materials are needed which combine the effects of low loss, high conductivity and allow the use of alumina filler for reliable strength.
The present invention fills such a need by providing new glass chemistries which exhibit controlled crystallization with alumina filler to form ceramic exhibiting good strength, silver and gold compatibility, and low loss. In addition, the new glasses allow for low temperature firing, e.i., below the melting point of silver which broadens the processing latitude of present day systems.